The invention concerns a linear rolling bearing comprising a plurality of ball circuits that are arranged behind one another in peripheral direction around a guide rail, at least one ball circuit, comprising a load-bearing section, a returning section and two deflecting sections which connect these load-bearing and returning sections to each other, being retained in a segmental cage housing that is formed by an inner cage part and an outer cage part, a load-being raceway element being fitted into a through-aperture of the outer cage part, and balls of the load-bearing section being supported on one side on a raceway of the load-bearing raceway element, which balls project through a slot of the inner cage part and are supported on another side on the guide rail for rolling in a longitudinal direction of the guide rail.
The ball circuit of such a bearing possesses an optimum adaptability to changing conditions of operation, like flexions, and to locally differing conditions such as, for example, non-circularity of the guide rail. The balls, the load-bearing raceway elements and also the ball-returning raceways always align themselves to the guide rail so that the advantages of a low displacing force and a quiet, smooth-running and low-friction bearing that is practically maintenance-free are obtained.
A linear rolling bearing of the pre-cited type for movement along a shaft is disclosed in the document WO 97101 713. In this bearing, three segmental cage housings are arranged directly next to one another in peripheral direction and require inter-engaging structures on their adjoining contact surfaces. If one of the segmental cage housings is removed, the other two housings lose their firm retention in peripheral direction.
Another linear rolling bearing is known from the document DE 42 10 039 A1 in which several segmental cage housings are arranged immediately adjacent to and behind one another in peripheral direction of a guide rail. To enable an adaptability of the load-bearing raceway elements to the guide rail, the peripherally successive segmental cage housings comprise elastic tongues that they are supported resiliently adjustable on one another. To obtain a coherence of all the segmental cage housings, two end, annular retaining elements are required. Therefore, in this case too, if the retaining elements are removed and one of the segmental cage housings is taken out, the rest of the housings lose their firm retention. The replacement of an individual housing is therefore rendered more difficult.
The document WO 98/21 494 shows a one-piece cage bushing with outwardly accessible spaces for lodging ball circuits and load-bearing raceway elements, so that the possibility of replacing individual ball circuits with their raceways in a simple manner does not exist.
The object of the invention is to provide a bearing which permits an insertion of individual segmental cage housings into the bearing and their replacement when, the bearing is in a mounted state on the guide rail without detriment to the optimal positioning of the segmental cage housings on the guide rail and to their mobility or retaining function during transportation.
This object is achieved according to the invention in that each segmental cage housing can be separately inserted and removed in radial direction from a recess of a circular cylindrical cage bushing surrounding the guide rail. The cage bushing comprises recesses that are accessible from its outer periphery and into each of which a segmental cage housing can be inserted in radial direction of the guide rail.
The inner cage part can comprise on each of its two ends pointing in longitudinal direction of the guide rail, a protruding knob which is snapped into a corresponding recess of the cage bushing. In this way, the individual segmental cage housings are suspended in the cage bushing so as to be freely movable independently of one another. The suspension of the housings in the cage bushing is effected by the knobs and cavities provided for this purpose.
The cage bushing can comprise spring lips each of which extends into one of the recesses and acts in radial direction of the bushing on the snapped-in knob. Each spring lip presses the segmental cage housing concerned even in the unloaded state against the guide rail so that the position of the housings is defined. When load alternation or a sudden application of operational load takes place, all the segmental cage housings are already in their correctly aligned positions. This contributes particularly to avoiding a rattling of the bearing components.
As can be seen in the drawings, each individual housing can possess full mobility (through 360xc2x0) about an imaginary axis Axe2x80x94A extending through the two associated recesses for the knobs. Their mobility about an imaginary axis Bxe2x80x94B that extends radially from the guide rail through the center of the load-bearing raceway element (axial alignment) is restricted as is also their mobility about an imaginary axis Cxe2x80x94C that extends tangentially of the guide rail in each case and centrally through the load-bearing raceway element concerned. The mobility in the radial direction of the guide rail is likewise restricted. This partial or restricted mobility results from the fact that the recesses have a larger diameter than the inserted knobs. Due to the force action chain xe2x80x9cloaded ballsxe2x80x94load-bearing raceway elementxe2x80x94segmental cage housingxe2x80x94unloaded ballsxe2x80x9d each housing adjusts itself to the guide rail fully independently of the other segmental housings. Since the individual segmental housings can move so as to adapt themselves to the shape of the guide rail, a simultaneous motion of the segmental cage housings is produced relative to a machine housing in which the cage bushing is received. This is made possible by the fact that the load-bearing raceway element has a back that is rounded in two directions and can therefore roll on the inner bore surface of the machine housing in which they are situated.
The load-bearing raceway element does not have to have only one groove but a plurality of parallel raceways for balls of the load-bearing sections can be configured thereon. The manufacture and mounting of the segmental cage housings are simplified if the outer cage part of each segmental cage housing is configured as a plastic part injected onto the load-bearing raceway element. The exactly defined seating of the load-bearing raceway element in the segmental housing results in an improved ball circulation (less noise generation), a precise jerk-free guidance of the balls when entering the loaded region and a reduction of the displacing force pulsation. It is therefore no longer necessary to configure special lead-in geometrical shapes (lead-in phases) on the ends of the load-bearing raceway elements. It is also possible to inject the segmental cage housing comprising an outer cage part and an inner cage part onto the load-bearing raceway element to form a one-piece plastic component. Injection or integral shaping reduces the number of parts to be mounted.
Due to the one-piece structure of the load-bearing raceway element and the segmental cage housing, a force-locked connection is obtained that makes it possible to incorporate parts of the ball deflecting sections that are configured in the injected plastic component into the load-bearing region. Thus, the transition xe2x80x9cball deflectionxe2x80x94load-bearing racewayxe2x80x9d can be configured in radial direction of the guide rail so that a step or a ramp higher than the load-bearing raceway element is formed in the unloaded state in the plastic component. The step or ramp must be dimensioned so that, taking into account the different depths of penetration of the balls into steel and plastic, the step or ramp disappears under load.
The cage bushing can have two end rings extending in planes vertical to the longitudinal direction of the guide rail, pairs of substantially parallel slots forming resilient regions being arranged on each end ring. Each segmental cage housing is then retained on its two end surfaces oriented in longitudinal direction of the guide rail by two corresponding resilient regions of the two end rings. The segmental cage housings can be retained in the cage bushing, for example, by end knobs that are inserted into apertures of the resilient regions. However, it is also possible to fix the segmental cage housings on the resilient regions of the cage bushing by glued or welded end surfaces. In this way, a system of inserting the segmental cage housings into the cage bushing is obtained which assures the mobility of the individual housings and offers protection against rotation, so that the housings are always in a defined position before the filled cage bushing is pushed onto the guide rail. Besides this, the system operates lash-free and permits a defined biasing of the segmental cage housings. The housings are biased either in a direction toward the guide rail or away from the guide rail toward the machine housing in which the cage bushing is lodged.
To obtain a linear rolling bearing requiring no or only very little maintenance, the segmental cage housings can comprise in the region of the load-bearing section for the balls and/or in the returning section for the balls, hollow spaces forming grease reservoirs.
A permanent, firm coherence of the segmental cage housings can also be obtained in that the inner cage part comprises side recesses into which side knobs of the outer cage part that is inserted into the inner cage part snap.